1. Field of the Invention
The present invention relates to a polishing apparatus and a polishing method and, more particularly, to a polishing apparatus and polishing method of a wafer in an inert gas atmosphere. Furthermore, the present invention relates to a polishing apparatus, a polishing method and a wafer evacuation program and, more particularly, to a polishing apparatus, a polishing method and a wafer evacuation program which evacuates a wafer when some trouble occurs during the working of the wafer.
2. Description of the Related Art
In recent years, owing to the development of semiconductor technology, progress has been made in the miniaturization of design rule and the trend toward multi-layer interconnection. Usually, a Cu damascene structure formed on the surface of a semiconductor wafer is such that a Cu film which is an interconnect film is formed on the surface, a TaN film or a Ta film which is a barrier film is formed under the interconnect film, and an oxide film is further formed under the barrier film. For this reason, in the chemical mechanical polishing (CMP) of Cu, polishing is performed by two steps, i.e., the Cu film is first removed by polishing and the barrier film, such as a TaN film, is then removed by polishing.
A wafer to be polished is taken out of a dedicated cassette by use of a handling device such as an indexing robot, and is then transferred to the polishing step to remove the Cu film and TaN film via a film thickness measuring step. If the step of removing the Cu film is called the first step and the step of removing the TaN film is called the second step, then in the Cu removal step, which is the first step, polishing is finished when TaN appears after the removal of Cu and the working proceeds to the second step. In general, in the TaN removal step, which is the second step, slurry which enables TaN to be relatively well polished is used. Therefore, the first and second steps are not performed by use of the same polishing pad and are carried out by means of separate polishing devices. After the polishing of the second step is performed, the wafer passes through a rough cleaning step for removing the polishing slurry and polishing powder, a precision cleaning step, a rinse step and a drying step and is housed in a dedicated cassette via the film thickness measuring step again.
In the wafer transfer step after this polishing step, during the rough cleaning step, the precision cleaning step, the rinse step, the drying step and the film thickness measuring step, the wafer surface after polishing may be oxidized and modified, posing a problem. In particular, metal materials such as Cu, Al and W which are used as conductors of wiring materials have the characteristic that portions in contact with the outside air are apt to be oxidized. In recent years, because interconnect portions are made fine, the surface area is large for the sectional area. This oxidation of the surfaces of wiring materials results in a substantial decrease in the conductivity and high-frequency characteristics of interconnects, exerting a great influence on the quality of final products. For example, if the interconnect width and interconnect depth of Cu, which are at present on the order of 0.1 μm, will become finer in the future, it might be thought that the degree of oxidation of the surfaces of wiring materials will pose a big problem.
Furthermore, in a case of retention of a product due to a trouble in the apparatus or work in the wafer polishing step, the oxidation or modification of the wafer surface proceeds, yielding the irregularity that the wafer quality is made worse thereby.
In the polishing step of the wafer surface, polishing slurry which performs fine etching by chemically reacting with a wiring material which is the film to be polished, such as Cu, is used. Also is used a cleaning chemical solution which performs fine etching by chemically reacting with a wiring material which is the film to be polished, such as Cu. It is necessary to very stringently control the time for which such a polishing slurry and cleaning chemical solution react with the wafer surface. If a wafer is left immersed in such a solution for a long time, the surface of the wafer is chemically modified by the etching of copper etc., bringing about a decrease in the conductivity of interconnects and in some cases causing troubles such as a breakage of interconnects, with the result that defective goods are produced.
Examples of such a conventional CMP system are described in the following literature, etc. However, no consideration is given to the oxidation and modification of surfaces. Reference material: The Latest CMP Process and Material Technology, Supervised by Toshiro Doi and Masaharu Kinoshita, Technical Information Society, p.257, p.261, p.272, etc. Reference literature: Electronic Materials, VOL. 40, No. 3, p.96, etc.